1. Field of the Invention
The present invention relates to an electronic device for playing back a content while managing the right of the content, and specifically to a technology for making confirmation on and updating the right of the content.
2. Description of the Related Art
With the aim of providing a variety of use forms of contents, a technology for allowing content providers to control the rights of users on the use of the contents has become popular. Such a technology is called DRM (Digital Rights Management). As one example, the OMA (Open Mobile Alliance) DRM standard has been formulated.
In such a DRM technology, the right information which is used to manage the user's right needs to be updated according to the use of content by the user. The Patent Document 1 identified below, for example, discloses a technology for controlling the playback of a content, for which the playback deadline has been set, and the update of the right of the content.
Meanwhile, in recent years, the OMA DRM R2 standard has been formulated. In this standard, “accumulated” is defined as a method for managing the total time of content playback. According to this method, a content is permitted to be played back with an electronic device until a total time of playback of the content reaches an upper limit that is preliminarily set by the right owner. And when the total time of playback has reached the upper limit, the playback is stopped. The above-mentioned OMA DRM R2 standard requires that the playback should be stopped “as accurately as possible in time”.    Patent Document 1: Japanese Patent Application Publication No. 2005-301634    Non-Patent Document 1: “Protecting Software from Inverse Analysis and Modification”, Nikkei Electronics, Jan. 5, 1998, pp. 209-220    Non-Patent Document 2: “Technology for Making Software Tamper-Resistant”, Fuji Zerox™, Technical Report No. 13, pp. 20-28.